Slug type inertia switch



April 6, 1965 w. w. H. CLARKE 3,177,312

SLUG TYPE INERTIA SWITCH Filed D90. 31, 1962 IN1/aura@ United StatesPatent O 3,177,312 SLUG TYPE lNERTlIA SWHTCH Walter W. H. Clarke, Kingswood House, East ll-lill,

Welling, Surrey, England Filed Dec. 3l, i962, Ser. No. 248,696

Claims priority, application Great Britain, dan. 9, i962, 354/62 8 llairns. (Cl. 26d-61.49

This invention relates to electric switches and more particularly to switches operable to close an electric circuit when a device to which the switch is attached is subjected to an accelerating or decelerating force.

Accordingly there is provided a switch operable to close an electrical circuit when an accelerating or decelerating force is applied to a device to which the switch is attached, comprising a body, a slug movable within a cavity in said body and means for initially retaining said slug in the bottom oi the cavity so that application of said force causes the slug to move towards that portion of the body forming the top of the cavity to close said circuit.

l prefer to shape the side wall of the cavity and the slug so that the latter hinges about the side wall on application of said force.

So that the switch may be used 1n rotating dev1ces subjecting the switch to centrifugal forces, the slug `1s disc-shaped the means for initially retaining the slug inthe bottom of the cavity exerts a force which retains the slug on the bottom of the cavity Whilst allowing it to slide thereover to contact the side wall when the switch is subjected to centrifugal forces.

in order that the invention may be fully understood, preferred embodiments thereof will now be described with reference to the accompanying drawings in which:

FlGURE l shows a sectional view of a preferred embodiment of the present invention, and y FGURE 2 shows a sectional view of a mcdiiication of the switch shown in FlGURE l.

in FIGURE l a switch Il has a body 2 comprising an electrically conductive annulus 3 having a cylindrical inside wall d held between an insulating ring 5 and an electrically conductive top plate d and a laminated plate 'i' comprising a space-r' ti, a magnet 9 and a backing plate ld. The spacer d, annulus 3 and top plate d, together form a closed cavityll` within the body 2 which contains a disc shaped electrically conductive slug l2. yThe slug l2 is initially retained on the bottom of the cavity lll formed by the spacer S by the magnetic force exerted by the magnet The diameter of the slug l2 is less than that of the inside diameter of the annulus 3. Secured to the plate d is an electrical contact wire i3, another contact wire ld being passed through and insulated iron the plate d to maire contact with the annulus 3. The ring 5 is also annular, its central aperture l5 being co-axial with the cylindrical inside wall l of the yannulus El. The upper and lower edges le and i7 respectively of the slug l2 are bevelled to provide an edge l which contacts the cylindrical inside wall l of the annulus 3 to provide a hinge point for the slug l2 as will be described in detail hereinafter.

The switch has been designed with such applications in mind as impact switches for artillery shells where high decelerating forces are encountered but it will be appreciated that such a switch may also be used in application where it is desired to close an electrical circuit when the device to which it is attached is subjected to accelerating or decelerating forces.

To take the example of an artillery shell which is subjected to spin by the riding of the gun barrel from which it is fired, the slug l2 will iirst be thrown against the side wall of the annulus 3 by the centrifugal force acting on the switch which is mounted at right angles to vquerlce bear the same reference numerals.

.il i 7,3 l2 Patented Apr. 6, llll the axis of the shell. The decelerating force experienced by the switch when the shell hits an object overcomes the force of the magnet 9 holding the slug l2 on the bottom of the cavity ll, to hinge the slug l2 about the edge 18 in contact with the side wall 4 ol the annulus 3 to take up a position in which the left hand side of the slug l2 is in Contact with the top plate d completing an electrical circuit through wire 13, top plate d, the slug l2, annulus 3 and wire i4.

The force exerted by the magnet 9 on the slug l2 may be varied by altering the thickness of the spacer ti so that the switch may be adjusted to operate in conditions in which only small decelerating forces are experienced.

FGURE 2 shows a switch Il@ having parts which are the same as those shown in FIGURE l, and in conseln FlGURE l, the slug l2 is retained in the bottom of the cavity lil by means of the magnet 9 `but in FGURE 2, a slug 3l is retained in the bottom of the cavity ll by means of a spring 32 clamped between the insulating ring 5 and annulus 3 from which the spring is electrically insulated. The spring may be a disc or a strip. The slug 3l is similar to slug l2 shown in FIGURE l but the top portion 33 of slug 3l is domed.

The operation oi the switch Pit? is the same as that of the switch l shown in FGURE l described earlier in this specification with the exception that the decelerating force experienced by the switch when the shell in which the switch is mounted hits object, causes the slug 3l to hinge about the edge l, the domed portion 33 deorrning the spring 32 to contact the top plate 6 and thus close the electr-ical circuit connected to wires i3 and le. To vary the value of the minimum decelerating force at which the switch will operate to close an electrical circuit, different springs may be used to provide different restrain ing forces on the slug 3l.

.electrically conductive material they may also be made of insulating material with metallic contacts or a layer of conductive material secured to the face of the top plate d forming the top of the cavity ll and the inside wall 4 of the annulus 3. j

The switch as shown in FlGURES l and 2 may be preencapsulated to precise dimensions in an epoxy injection mould tool, it then being suitable for putting into a nal assembly.

l claim:

l. An inertia switch comprising a body, opposed lirst and second end walls, a side wall interconnecting said end walls to form said body having a cavity therein, a conductive slug within said cavity, means for urging said slug against said iirst end wall for sliding movement there over and electrical contact means lon said second end wall and said side wall, said slug having a protruding edge which engages said side wall when encountering centrifugal force on rotation of the body to form a pivot for the slug, thereby permitting the slug to hinge about the pivot when encountering lonvitudnal deceleration or" the body to bridge said electrical Contact means and form a closed circuit between said electrical contact means on said end and side walls.

2. An inertia switch according to claim l wherein said urging means includes a spring in contact with said 'slug near said second end wall.

3. An inertia switch according to claim l wherein said slug is ci magnetic material and said urging means cornprises a permanent magnet mounted to retain said slug near said first end wall.

4. An inertia switch comprising a body, iirst and second end walls, a conductive side wall interconnecting said end walls to form said body with a cavity therein, a

conductive slug Iwithin the body, means for urging said slug againstl said iirst end wall for sliding movement thereover, means insulating the slug from the side Wall except on direct contact therewith, electric contact means provided on said second end wall and insulated fromv said sidewall, said slug having a protruding edge which engages said side wall when encountering centrifugal force on rotation of the body to form a pivot for the slug, thereby permitting the slug to hinge about the pivot when encountering longitudinal deceleration of the body to contact the conductive portions of the second end wall and the side Wall thereby to provide an electric current path between the side wall and the contact means on the second end wall.

5. An inertia switch comprising a body, iirst and second opposed end walls, the tirst end wall being electrically conductive and the second end wall being electrically nonconductive, an electrically conductive side wall interconnecting said end walls to form said body having a cavity therein, means insulating said side wall from said first end wall, an electrically conductive substantially cylindrically shaped slug within said cavity, means for urging said slug against said second end wall for sliding movement thereover, the circumference of said slug having an extending pivot edge which engages said side wall when responding to centrifugal force on rotation of the body to form a pivot point for the slug, whereby the slug hinges about the pivot on longitudinal deceleration of the body to contact the tirst end wall and thereby provide an electrical current path between the side wall and the rst end wall.

6. An inertia switch comprising a cylindrical body formed by an electrically conductive disc, an insulating ring, an electrically conductive annulus, an insulating disc-shaped spacer and a disc-shaped permanent magnet, secured together in co-axial alignment in that order to provide a cavity within said body, an electrically conductive ferro-magneticslug in said cavity held centrally on said spacer by the magnetic force exerted by said magnet, electrical leads secured to said electrically conductive disc and said annulus, said slug having a substantially cylindrical shape with a protruding circumferential edge for engaging the inside wall of said annulus when encountering centrifugal force on rotation 4 of said body about its longitudinal axis to form a pivot forl the slug, so that the slug hinges about the pivot when encountering longitudinal deceleration of the body thereby contacting the electrically conductive disc to provide a current path between said conductive disc and said annulus.

7. An inertia switch comprising a cylindrical body formed' by an electrically conductive disc, an insulating ring, a retainer spring, an electrically conductive annulus and ay disc-shaped bottom plate secured together in coaxial alignment in that order to provide a cavity within said body, said' spring being electrically insulated from said annulus, an electrically conductive slug in said cavity held centrally on said bottom plate by pressure of said spring, electrical leads secured to said electrically conductive disc and said annulus, said slug having a substantially cylindrical configuration with a protruding edge which engages the inside wall of said annulus responsive to centrifugal torce on rotation of said body about its longitudinal axis to form a pivot for the slug, so that the slug hinges about the pivotV when encountering longitudinal deceleration of the body to thereby contact the electrically conductive dise and provide a current path between said conductive disc and said annulus.

8. An inertia switch comprising a body with opposed first and second end walls, a side Wall interconnecting saidI end walls to form a cavity within said body, a movable slug within said cavity slidable over said irst end Y wall and having a protruding edge to engage the side wall when encountering centrifugal force on rotation of the body and to pivot thereon when encountering longitudinal deceleration of the body to urge said slug into contact with saidl second end wall, and electrical contact means on said second end wall operable to form a closed circuit when said slug is urged into contact therewith.

References Cited in the tile of this patent UNITED STATES PATENTS 2,458,478 Maneval Jan. 4, 1949 2,890,303 Clurman June 9, 1959 2,896,447 Phillips et al July 28, 1959 2,997,557 Gillmore et al Aug. 22, 1961 

1. AN INERTIA SWITCH COMPRISING A BODY, OPPOSED FIRST AND SECOND END WALLS, A SIDE WALL INTERCONNECTING SAID END WALLS TO FORM SAID BODY HAVING A CAVITY THEREIN, A CONDUCTIVE SLUG WITHIN SAID CAVITY, MEANS FOR URGING SAID SLUG AGAINST SAID FIRST END WALL FOR SLIDING MOVEMENT THEREOVER AND ELECTRICAL CONTACT MEANS ON SAID SECOND END WALL AND SAID SIDE WALL, SAID SLUG HAVING A PROTRUDING EDGE WHICH ENGAGES SAID SIDE WALL WHEN ENCOUNTERING CENTRIFUGAL FORCE ON ROTATION OF THE BODY TO FORM A PIVOT FOR THE SLUG, THEREBY PERMITTING THE SLUG TO HINGE ABOUT THE PIVOT WHEN ENCOUNTERING LONGITUDINAL DECELERATION OF THE BODY TO BRIDGE SAID ELECTRICAL CONTACT MEANS AND FORM A CLOSED CIRCUIT BETWEEN SAID ELECTRICAL CONTACT MEANS ON SAID END AND SIDE WALLS. 